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Cemented gangue backfill bodies (CGBBs) are characterized by high brittleness and poor toughness in backfill mining technology. According to different types of waste tires corresponding to different processing and crushing means, waste tire steel fiber (WTSF) was divided into S-WTSF, P-WTSF, and H-WTSF. The influence of CGBBs with different types and amounts of WTSF on the early mechanical properties of the modified samples was studied. Uniaxial compressive strength (UCS) and scanning electron microscopy (SEM) tests on the modified CGBB samples were carried out. The results show that as the WTSF content increased from 0% to 1.5%, the UCS of CGBB samples modified with S-WTSF, P-WTSF, and H-WTSF at a curing time of 3 d first increased and then decreased; the turning point for S-WTSF and P-WTSF was 1%, and the turning point for H-WTSF was 0.5%, whereas the UCS of these modified CGBB samples at a curing time of 7 d decreased continuously with the increasing addition of WTSF content. The addition of WTSF made CGBB samples change from brittleness to ductility. With the increasing content of S-WTSF and P-WTSF, the toughness of the modified CGBB samples at a curing time of 3 d first increased and then decreased (the turning point was 1%), and that at the curing time of 7 d continued to increase. The toughness of CGBB modified with H-WTSF first increased and then decreased (the turning point was 0.5%) with the increase of the H-WTSF content. The toughness enhancement mechanism of CGBB modified by WTSF can be illustrated from a microscopic perspective as follows: WTSF is wrapped by hydration products, and the inlaying and bridging effects of WTSF are formed in the CGBB matrix. This research provides a basis for the improvement of mechanical properties of CGBB modified by WTSF and a new method for the reuse of discarded tires. [ABSTRACT FROM AUTHOR]

Foam concrete is a porous cement-based material that could accommodate a high-volume particle addition at the mid- to high-density range (0.8 to 1.6 g/cm3). However, with low-density foam concrete (0.4 to 0.8 g/cm3), conventional particle inclusion (e.g., sand) tends to degrade the cellular microstructure and mechanical performance. Therefore, to improve low-density foam concrete, the novel use of crumb rubber (the rubber particles recycled from waste tires) in foam concrete is studied, as its unique attributes can potentially allow for the retention of structure and improved performance in foam concrete. The influence of no inclusion, sand, and crumb rubber on the microstructure and mechanical performance in foam concrete with the density of cellularized cement paste as 0.40 and 0.60 g/cm3 was studied. Computed tomography indicates that the inclusion of crumb rubber can mitigate the foam degradation concern associated with particle inclusion in low-density mixtures. A notable improvement was also observed in the mechanical properties of 0.40 g/cm3 rubberized foam concrete mixtures—compressive strength, plateau strength, and impact resistance—when referenced to the sand inclusion counterpart. [ABSTRACT FROM AUTHOR]

Based on the efficient resource utilization of scrap tires, pyrolysis carbon black (PCB), and pyrolysis oil of waste tire (TPO), scrap tires' products were treated using dry styrene-butadiene-styrene (SBS) polymer modification of asphalt. The products of scrap tires, PCB and TPO, were handled using dry SBS polymer modification of asphalt based on the effective resource use of scrap tires. The consequences of scrap tires, PCB and TPO, were taken using dry SBS polymer modification of asphalt based on the effective resource use of scrap tires. PCB and TPO composite effect seriously degraded. Based on this, the impact of dry SBS polymer modification on the functionality of PCB-TPO-modified asphalt and the mechanism of modification was examined. According to the investigation, the SBS polymer was evenly distributed and fully developed in the asphalt mixture, which significantly enhanced the qualities of asphalt and the asphalt mixture and performed a positive role in the internal structure of the asphalt mixture. [ABSTRACT FROM AUTHOR]

As a potential long-life pavement material, the high brittleness of epoxy asphalt prevents its application. Recycled from waste tires, crumb rubber (CR) can be used with styrene-butadiene-styrene (SBS) to prepare SBS/CR composite modified asphalt. The main objective of this paper is to conduct the material design of epoxy asphalt with SBS, CR, and core-shell rubber (CSR) to toughen the epoxy asphalt and enhance its performance. First, SBS modified epoxy asphalt and SBS/CR composite modified epoxy asphalt (CMEA) were prepared to optimize the toughening materials based on tensile tests. Subsequently, based on the optimized material, the optimal proportion was determined through the response surface method by the Design-Expert software. Third, the microscopic morphology of different epoxy asphalt was observed by laser scanning confocal microscopy (LSCM), and the changes in functional groups were tracked using Fourier transform infrared spectroscopy to reveal the toughening mechanism. Finally, the viscosity test was carried out on the optimal SBS/CR-CSR CMEA at different temperatures to determine its mixing temperature and allowable time. The results show that the SBS/CR-CSR CMEA is the best toughening method, and the optimal epoxy and CSR proportion is 37% and 12%, respectively. Its tensile strength increases by 467.11% and elongation at break increases by 68.73% compared with unmodified epoxy asphalt. The formation of interpenetrating polymer network structure between the SBS/CR network and epoxy resin network, as well as the change in the benzene ring that determines the softness and toughness, may be the main strengthening and toughening mechanisms. The suitable mixing temperature is 160°C for the optimal SBS/CR-CSR CMEA in this paper, which reduces about 20°C compared with conventional CR or SBS/CR composite modified asphalt, providing better environmental benefits. Overall, the SBS/CR-CSR CMEA presents a new solution for the promotion and application of epoxy asphalt. [ABSTRACT FROM AUTHOR]

Composite modification of an asphalt binder forms an interesting approach to enhance the properties over diverse performance regimes. Aging of asphalt binders during the production, construction, and service life of the asphalt mixtures in pavement increases its stiffness and may have a negative impact on their resistance toward fatigue and low-temperature cracking, thus generating the need to evaluate the aging behavior of a composite-modified asphalt binder. This study analyzed the aging characteristics of individual and composite asphalt binders produced with waste ethylene-propylene-diene-monomer (EPDM) rubber, derived from manufacturing units dealing with nontire automotive rubber products, and the tire pyrolysis oil (TPO) derived from the pyrolysis of scrap tires. Three different pathways were used to formulate composite-modified binders, namely, without pretreatment and with pretreatment through heat and microwave irradiation. The study focused on the evaluation of physical, rheological, chemical, and microstructural characteristics of the composite-modified binders produced in different manners after being subjected to both short-term and long-term aging. Results showed that the effect of aging was adverse on the base binder and the binder prepared with TPO alone. In contrast, the addition of EPDM rubber alone improved the binder's aging resistance. The composite-modified binder through the pretreatment yielded significantly improved performance against aging; thus, composite modification with pretreatment can be a useful approach to yield aging-resistant binders prepared by EPDM and TPO. [ABSTRACT FROM AUTHOR]

Crumb rubber (CR) from grinding waste tires has served as an asphalt modifier in asphalt pavement construction for decades. Incorporating CR in asphalt mixtures by the dry method is becoming popular with the emphasis on low carbon emissions, greenness, and sustainability. However, the poor compatibility and mechanical performance of dry-mixed asphalt rubber limit its application. This work presents the effect of practical activation treatments on the microstructure of CR and mechanical properties of the resulting asphalt binder and mixtures, aiming to modify CR surface features and improve the performance of asphalt mixtures. According to previous work, the activation treatment methods of high-temperature, preswelling, the two combinations, and microwave irradiation for CR were compared. Meanwhile, the surface morphology, chemical features, and dispersion degree of various activated CR as well as rutting resistance, low-temperature performance, and moisture stability of the resulting asphalt and asphalt mixtures were evaluated. The results indicated that selected activation methods significantly change the surface morphology and chemical features of CR, and the activated CR shows a flocculent structure with porous surface and reactivity. Preswelling with high-temperature and microwave activation for CR endows the modified asphalt with significantly improved viscoelastic properties. Preswelling with high-temperature activated CR asphalt shows better low-temperature cracking resistance. Asphalt modified with activated CR presents homogeneous and compatible states in microscopy compared with ordinary asphalt rubber. Incorporating activated CR in asphalt mixtures by the dry method is a promising technique in view of improved low-temperature cracking resistance and moisture stability. [ABSTRACT FROM AUTHOR]

Waste tire pyrolysis has the advantages of economy, environmental protection, and high energy conversion rate; however, there is little research on the application of pyrolysis carbon black (PCB), which accounts for a high percentage of pyrolysis products, in asphalt and asphalt mixtures. The objectives of this study were to investigate the effect of PCB ash on the physical properties of asphalt binders, the effect of coupling treatment on the dispersibility of PCB-modified asphalt, and the effect of mixing process on the road properties of PCB asphalt mixtures. The physical properties of co-pyrolytic carbon black (CPCB) and low-temperature vacuum pyrolytic carbon black (VPCB) blended with 70# base asphalt and styrene-butadiene-styrene (SBS)–modified asphalt (SBSMA) were evaluated. Mechanisms behind the differences in the dispersion of CPCB in asphalt were revealed. In addition, the road performance of different PCB asphalt mixtures was compared. The results indicate that the optimum admixtures of VPCB and CPCB in 70# base asphalt are recommended to be 20% and 10%–15%, respectively, and the optimum admixtures of VPCB and CPCB in SBSMA are 10%–25% and 10%–20%, respectively. Acid washing reduces the ash content of the CPCB surface, and coupling agent can promote the dispersion of CPCB in asphalt. The wet-prepared CPCB-modified asphalt mixtures showed overall better road performance than the dry-prepared ones. Dry CPCB asphalt mixtures with 50% cement instead of equal mass of mineral powder have the potential to replace the wet process. [ABSTRACT FROM AUTHOR]

The main objective of the current study is the recycle of end-of-life tires as fine aggregate in the production of fly ash–based geopolymer composites. Moreover, it aimed to improve some adverse characteristics caused by the recycled fine aggregate named crumb rubber of such composites by changing the binder content of the composite mixture. In this regard, four crumb rubber replacement levels of 10%, 20%, 30%, and 40% were designated in the production of rubberized geopolymer composites. The main mixtures were designed at a binder content of 600 kg/m3. Herein, it should be stated that in the current study, the term binder content was considered a total of precursor (aluminosilicate-rich raw material) and alkaline activator. According to the performance of the geopolymer composites, the binder content was increased to first 700 kg/m3 and then 800 kg/m3. Thereby, twelve crumb rubber incorporated and three plain fly ash–based geopolymer composites were designed and produced in this study. The performance of these composites was evaluated in terms of fresh and hardened state properties. As fresh state properties, the flowability and fresh unit weight were tested while as hardened state properties, dry unit weight, compressive and splitting tensile strength, total and capillary absorption capacities, and thermal conductivity were tested. The results revealed that replacing river sand with crumb rubber remarkably influenced the characteristics of geopolymer composites. The flowability, unit weights, strength performance, and thermal conductivity of geopolymer composites decreased whereas the absorption capacity increased. Increasing binder content became a remedy for some characteristics of composites. As a consequence, it can be stated that this waste material can be used in the production of such composites but in a controlled manner. [ABSTRACT FROM AUTHOR]

The application of waste tire rubber in the concrete industry is one of the most effective and environmentally friendly ways to solve the problem of so-called black pollution. However, the application of rubber particles (RP) in the concrete industry is hindered by their low stiffness and poor bonding performance with the cement matrix. In this paper, a novel modification method of polydopamine (PDA) modification was used to enhance the hydrophilicity of the RP surface. The surface morphology, element content, and hydrophilicity of RP treated with PDA and KMnO4 were analyzed through scanning electron microscope and energy dispersive spectrometer (SEM-EDS) and sedimentation methods. The unit weight, ultrasonic pulse velocity (UPV), compressive strength, compressive toughness, toughness index, and flexural strength were taken to determine the mechanical properties of ultrahigh-performance rubber concrete (RUHPC). The results showed that the adhesion between paste and RP and the sedimentation rate of RP with PDA or KMnO4 treatment methods exhibited a remarkable improvement. Compared with unmodified RUHPC, the basic mechanical properties of KMnO4 -modified RUHPC were improved slightly, and its toughness index was improved greatly. SEM and EDS results confirmed that PDA was deposited on the surface of RP, eliminating the gap of interface transition zone and significantly enhancing UPV, compressive strength, and flexural strength of RUHPC by 4.1%–5.8%, 17%–20%, and 6.1%–9.8%, respectively. In addition, the compressive toughness of unmodified and KMnO4 -modified RUHPC decreased, whereas that of PDA-modified RUHPC increased significantly. It can be concluded that the mechanical properties of RUHPC with treated RP have improved significantly and the application of RP in ultrahigh-performance composites (UHPC) offers more opportunities for recycling RP. [ABSTRACT FROM AUTHOR]

Rubber-coated ballast (RCB) is a new innovative ballast aggregate obtained by coating natural aggregates with recycled crumb rubber by using polyurethane binder. The objective of RCB is to reduce the ballast degradation, thereby reducing the deterioration of rail track geometry and also maintenance costs. Natural ballast; crumb rubber of sizes 0.4, 0.8, and 2 mm; Elastan polyurethane; and geogrid (triangular, 69 mm aperture size) were used in this study. The results of abrasion, impact value, and soundness tests show that RCB has a higher resistance to abrasion, impact, and weathering compared to natural ballast. Subsequently, the shear behavior and particle breakage of natural ballast, RCB, unreinforced, and geogrid-reinforced RCB–natural ballast mix was explored using the large-scale direct shear apparatus at different normal stresses and shearing rates (Sr). The test results indicate that due to rubber coating the peak friction angle (φ) of RCB samples reduces as compared to natural ballast. The reduction in φ of RCB samples is attributed to a change in surface texture. Moreover, 0.4-RCB (RCB made with rubber crumbs of size 0.4 mm) shows the least reduction in φ compared to 0.8-RCB and 2-RCB (RCB made with rubber crumbs of size 0.8 and 2 mm). It was further observed that with the increase in proportion of 0.4-RCB in geogrid-reinforced natural ballast both the peak friction angle and particle breakage (Bg) of ballast decreased significantly. The current study established the optimum content of 0.4-RCB to be mixed with geogrid-reinforced natural ballast to be in the range of 44%–53%. The problem of excessive degradation of ballast particles and the associated changes in the track geometry owing to the repeated application of heavy axle loads is addressed by coating the natural ballast with crumb rubber generated from waste tires. The rubber-coated ballast (RCB) is found to offer better abrasion, impact, and weathering resistance when compared to natural ballast. Moreover, it undergoes negligible particle breakage under direct shear conditions. The decrease in the extent of particle breakage helps in reducing the frequency of ballast replacement operations and hence tracks maintenance costs. Furthermore, RCB, when reinforced with geogrid, offers better shear strength than that of natural ballast alone. These observations imply that the tracks with geogrid-reinforced RCB can effectively reduce the risk of track instability. [ABSTRACT FROM AUTHOR]

Low-carbon environmental protection and reduction of pollution have become development goals for asphalt pavement. Crumb-rubber modified asphalt binder (CRAB) made from recycled scrap tires provides an economical and practical way to salvage the natural raw materials but results in carbon and toxic emissions. Warm-mix technology has been applied to recycled CRABs, forming warm-mixed crumb-rubber asphalt binders (W-CRABs) as effective and efficient green materials to reduce energy consumption and mitigate environmental pollution. In addition, the type and dosage of warm-mix additives are key factors affecting rutting and cracking pavement distress. This study aims to correlate Superpave protocol results with those of fractional viscoelastic models to estimate the high- and low-temperature properties of W-CRABs, including recycled crumb rubber, viscosity reducer (1%, 2%, 3%), and surfactant (0.4%, 0.6%, 0.8%). Bending beam rheometer and dynamic shear rheometer tests were performed to determine experimental parameters such as complex modulus, phase angle, and the ratio of creep rate to creep stiffness (m/S). The fractional derivative model (a connection composed of one spring, one linear dashpot, and two Abel dashpots in series) and the generalized fractional viscoelastic model (a combination of two spring-spot fractional elements in series) were developed to investigate viscoelasticity of W-CRABs. In conclusion, by experimental and modeling methods, this study recommends that, for northwest China with significant temperature differences, the optimal resistance to cracking and rutting can be achieved by mixing 0.6% surfactant and CRABs. [ABSTRACT FROM AUTHOR]

Due to the fast-growing number of cars, the amount of scrap tires is quickly increasing across the world. Because buried tires need a long period of time to dissolve, the accumulation of scrap tires in different countries has caused several social, economic, and environmental issues worldwide. Many researchers in geotechnical engineering have utilized scrap tires in various forms for soil reinforcement in recent years. A by-product of waste tire processing is waste tire textile fiber (WTTF). These WTTFs are classified as special wastes, and they are frequently buried or burned in violation of international law. This study experimentally shows that these materials could be recycled and mixed with soil to improve the mixture mechanical properties. A complete series of small-scale laboratory tests, including direct shear test, Brazilian tensile test, permeability test, and swelling test, was conducted to examine the possibility of reusing WTTFs as soil-reinforcing agents. Five different fiber percentages (FPs), i.e., 0%, 0.5%, 1%, 2%, and 4%, of soil dry weight were mixed with the soil and the mechanical behavior of the mixture was investigated. The test results suggest that adding fiber to the soil improves both its shear and tensile strengths. The material ductility increases by adding the fiber to the soil as well. Further, the soil mixed with the fiber has a greater permeability coefficient and has less swelling potential. The mixture with these improved mechanical properties can cause less lateral pressure in case of being used as a backfill material. As a result, rather than being buried or burned, these wastes could be utilized to enhance the mechanical properties of various types of soils in geotechnical applications. The testing procedures and results are reported, discussed, and compared with those from the literature. [ABSTRACT FROM AUTHOR]

High-performance concrete (HPC) is known as a material of high strength and high durability. This investigation is focused on the influence of the use of rubber waste tires on the physical, mechanical, and durability characteristics of HPC. Tire-rubber residues were used in the contents of concrete at 7.5%, 15%, and 30% in relation to the sand mass. Eleven mixtures were tested in the experimental program. To improve the mechanical strength of rubberized concrete, superficial treatment of the rubber was carried out with calcium carbonate and silica fume. From the results obtained, the following are notable: reduction of the area between the rubber and the cement paste, increased resistance to compression and traction of the concrete with treated rubber, and lower water absorption value and void index, evidencing the benefit of this type of surface treatment. Regarding the durability, electrical resistivity, chloride ion penetration, and carbonation tests, high-strength rubberized concrete shows the potential to be used in aggressive environments. [ABSTRACT FROM AUTHOR]

Waste ethylene-propylene-diene monomer (EPDM) rubber and tire pyrolytic oil (TPO) derived from waste tire pyrolysis have shown promising results for their use in asphalt binder modification. However, their incorporation has shown improvements mainly either on rutting or fatigue behavior of the resultant asphalt binders. Composite modification may be a viable option to achieve improved performance with these two materials. The aim of this study was to evaluate the rheological, morphological, and chemical properties of asphalt binders produced through both individual and composite modifications using waste EPDM rubber and TPO. For composite modification, two different blending schemes were used: (1) sequential addition of TPO and EPDM rubber to the heated base asphalt binder; and (2) premixing of TPO and EPDM rubber prior to addition to the heated base asphalt. In the latter case, before being added to the base asphalt, TPO premixed EPDM rubber was conditioned at two temperatures (25°C and 90°C) to see the effect of different conditioning temperatures in composite modification. Firstly, the conventional properties of all the binders in the unaged state were assessed, followed by the evaluation of short-term-aged binders for Superpave and Shenoy rutting parameters, frequency sweep, zero shear viscosity, multiple stress creep and recovery, and Burger's modeling. The long-term-aged binders were evaluated through the Superpave fatigue parameter, Glover-Rowe parameter, and linear amplitude sweep. Fourier transform infrared (FTIR) spectroscopy and optical microscopy were used for chemical and morphological analyses. The premixing of EPDM and TPO accompanied with conditioning at 90°C imparted a synergistic effect with improvements in both rutting and fatigue performance of binder. The improvement in performance attributes was ascribed to the preswelling of EPDM rubber with TPO, which was evident from the morphological analysis. FTIR provided evidence of chemical interaction between EPDM rubber and TPO during the conditioning and blending processes. [ABSTRACT FROM AUTHOR]

This paper presents the potential of scrap tire in controlling the onset of instability of sand in the constant shear drained (CSD) stress path. A series of triaxial tests in the constant shear drained stress path was conducted on the sand and sand––tire chip (STCh) mixtures. All the tests were performed following the conventional consolidated drained (CD) test up to a predefined deviator stress (onset of CSD). The CSD test then was carried out on samples at the onset of CSD by reducing the confining pressure while maintaining the deviator stress and backpressure constant. The effect of different deviator stress (qCSD), initial mean stress (po′) levels, and tire chip content (TCh) on the onset of instability were investigated. The instability of sand and sand–tire chip mixtures was determined based on the decrease in the constant deviator stress (dq<0) and second-order work criteria (d2W<0). Both approaches were found to be consistent in determining the onset of instability of STCh mixtures. The onset of instability of sand is influenced by the TCh content and qCSD. On other hand, a unique value of pf′ was found for different values of po′. The optimum performance in controlling the onset of instability of sand was found for TCh=20% for the tire chip considered in this study. The mobilized effective friction angle also exhibited improved performance for TCh = 20%. In addition, the modified state parameter had good correlation with the mobilized effective friction angle in the CSD stress path. [ABSTRACT FROM AUTHOR]

With the increasing number of vehicles plying on the roads, alarming volumes of the waste tires are generated every year throughout the globe. The disposal of these materials is of great concern. The most efficient way to reduce their volume is to reuse these materials for various applications. To investigate the behavior of the scrap tire derivatives under cyclic load, a series of cyclic triaxial tests were conducted. Seven different mixes of sand and tire crumbs (by weight) were tested under three different confining pressures (50 kPa, 75 kPa, and 100 kPa) and four different shear strain amplitudes (0.075%, 0.15%, 0.225%, 0.3%). All the tests were reported for 200 loading cycles. The result showed that the addition of tire crumbs reduced the shear modulus and increased the damping ratio. The addition of tire crumbs reduced the modulus degradation rate remarkably and makes the material useful for structures subjected to cyclic loading. The resistance toward liquefaction is also increased drastically upon the addition of tire crumbs, and the mixes showed high resistance toward the generation of excess pore water pressure. The detailed characterization of sand-tire crumbs mixes reported in the present study can be very helpful when choosing the mix for different applications. [ABSTRACT FROM AUTHOR]

Research on waste tire pyrolysis carbon black (PCB) in bitumen mixtures indicates that it has excellent high-temperature rutting resistance; however, the degradation of low-temperature crack resistance and water stability of PCB-modified asphalt limits its wide application. Therefore, the low-temperature crack resistance and water stability of PCB-modified hot-mix asphalt (HMA) were enhanced by addition of waste chicken feather (WCF). Based on the response surface methodology (RSM), a variance analysis (ANOVA) and P-value test of the model response coefficient were carried out, and the performance prediction models of percentage air voids (VV) in bituminous mixtures, 30-min Marshall stability (MS), and 48-h MS were obtained. The interaction effects of different independent variables on response variables were analyzed. In addition, the optimal solutions of multiresponse variables obtained by the response optimizer were 0.20% PCB content, 0.36% WCF content, shearing time of 5.78 min for WCF, and 6.66% asphalt–aggregate ratio. The corresponding performance index prediction values were 4.00% VV, 12.80 kN 30-min MS, and 12.65 kN 48-h MS. The road performance test results demonstrated that incorporating WCF improved the high-temperature rutting resistance, low-temperature crack resistance, and water stability of PCB-modified hot-mix asphalt. This study provides a precise performance prediction model for adding PCB and WCF to HMA. [ABSTRACT FROM AUTHOR]

Use of scrap tire derivatives for civil engineering applications is an emerging field. In spite of extensive characterization of these materials, most of the studies focused on smaller-sized tire derivatives, i.e., tire crumbs. Furthermore, only a few studies are available on the cyclic response of these tire derivatives. The present study details the dynamic properties and liquefaction behavior of tire chips and sand–tire chip mixes. A series of strain-controlled cyclic triaxial tests were carried out considering confining pressure, strain amplitude, and tire chip content as variables. The tests were performed on seven different mixes with varied proportions of sand and tire chips by weight. The addition of tire chips to the sand increased the liquefaction resistance and threshold shear strain of the mixes significantly. The addition of the tire chips decreased the shear modulus and increased the damping ratio of the mixes. Furthermore, based on the behavior of the mixes with different tire chip contents, an optimum mix was suggested. [ABSTRACT FROM AUTHOR]

This study evaluated tire pyrolytic oil (TPO) derived from waste tire pyrolysis as a rejuvenating agent for three types of aged asphalt binders (unmodified, polymer-modified, and crumb rubber–modified). Gas chromatography–mass spectrometry (GC–MS) was performed to identify chemical compounds present in TPO. The rheological characteristics of all binders were examined through the complex viscosity–frequency profile, zero-shear viscosity, failure temperature, Black space diagrams, Cole–Cole plots, Superpave fatigue parameter, Glover–Rowe parameter, and linear amplitude sweep (LAS) tests. Mass loss was also determined for the rejuvenated binders. All binders were subjected to Fourier transform infrared (FTIR) analysis, and sulfoxide and carbonyl indices were computed. Atomic force microscopy (AFM) was conducted to study the effect of TPO on the micromorphology of the binders. The normalized Euclidean distance approach was used to rank the rejuvenated binders with respect to the proximity of their rheological and FTIR characteristics to that of the unaged binder. The use of TPO as a rejuvenating agent enabled the aged binders to achieve properties comparable to those of the unaged asphalt binder. The AFM-based rejuvenation index (RI) indicated a good potential of TPO as a rejuvenator. The results of the binder rheological parameters and the FTIR indicators investigated in the study indicated that a 9% dosage of TPO as a rejuvenating agent was the most effective. [ABSTRACT FROM AUTHOR]

The asphalt modifier formed by the miscibility of waste cooking oil and rubber is referred to as WRO. WRO modifiers prepared from waste tire crumb rubber (WTCR) and waste cooking oil (WCO) have the potential for solving the problems of segregation of rubber asphalt and the low recycling rate of waste cooking oil. The results of the Cole-Cole curve show that the WRO modifier can remarkably enhance the miscibility of WTCR and base asphalt. The Fourier transform infrared spectrometer (FTIR) tests proved that WTCR, WCO, and base asphalt were mainly physically miscible during the preparation of the WRO modifier and modified asphalt. In the process of preparing the WRO modifier and modified asphalt, the rubber undergoes devulcanization, conjugated double bond reduction, and oxidation reactions. The WRO modified asphalt presents great workability, storage stability, high-temperature elastic recovery, low-temperature crack resistance, and deformation recovery ability. In addition, the results of the multiple stress creep and recovery (MSCR) tests present that the WRO modified asphalt has desirable antirutting properties. The optimal preparation process of the WRO modifier preferred by orthogonal design is stirring 0.5 h at 260°C, and the mass ratio of WTCR and WCO is 6∶4. [ABSTRACT FROM AUTHOR]

Pyrolysis technology is receiving growing attention for managing postconsumer tire and plastic waste streams. Pyrolytic char is generated as a byproduct in the pyrolysis process and faces challenges regarding its stable and reliable reuse. The use of tire pyrolytic char (TPC) and plastic pyrolytic char (PPC) has recently gained interest in asphalt binder modification, which can be a feasible and attractive alternative for their utilization. The present study focused on a multifaceted investigation at three levels: (1) characterization of the pyrolytic chars (TPC and PPC), (2) characterization of asphalt binders modified with different dosages (0%, 5%, 10%, 15%, and 20%) of TPC and PPC focusing on conventional, rheological, microscopic, and thermochemical tests, and (3) mechanical characterization of asphalt mixtures fabricated with TPC- and PPC-modified binders in terms of rutting, moisture damage, and fatigue performance. Leachate toxicity was also evaluated to ensure that the use of TPC and PPC in asphalt mixtures is safe for the environment. Results showed that both TPC- and PPC-modified binders and mixtures showed better rutting resistance than the control binder and mixture up to 20% dosage. Fourier transform infrared (FTIR) spectroscopy showed that TPC and PPC interacted chemically with the base binder during modification. Leaching tests indicated that TPC and PPC could be safely used in asphalt mixtures for pavement construction. Comparing the fatigue and moisture damage results, it was found that the optimum performance was achieved at a 10% dosage of both TPC and PPC. This observation was consistent with fatigue tests on binders and asphalt mixtures. [ABSTRACT FROM AUTHOR]

Pyrolysis is being employed as a viable option for the disposal of different industrial and agricultural wastes, including end-of-life vehicle tires. Tire pyrolytic char (TPC), a solid fine carbonaceous material obtained as a by-product during the pyrolysis of waste tires, is gaining interest among pavement researchers for its use in asphalt binder modification. Good storage stability is essential to ensure that a modified binder retains the desired properties after its fabrication. Cross-linking agents are frequently used to enhance the storage stability of modified binders. This study characterized the storage stability performance of TPC-modified binders with and without the incorporation of cross-linking agents. Bituminous binders modified with TPC were analyzed for storage stability at multiple dosages of two widely used cross-linking agents: polyphosphoric acid (PPA) (0.5%, 1.0%, and 1.5%) and sulfur (0.15%, 0.3%, and 0.45%). In addition to softening point difference (SPD), separation indices (SIs) derived from frequency sweep, temperature sweep, and multiple stress creep and recovery (MSCR) tests were employed to characterize the storage stability. Compatibility evaluation was also done through Cole-Cole plots. Fourier transform infrared spectroscopy (FTIR) was used to study the storage stability through the changes in binder spectra. Remixing of the TPC-modified binders was also performed to assess the retrieval of homogeneity in a segregated TPC-modified binder. All the SIs were measured and compared for binder specimens before and after remixing. Binders were ranked based on the SIs, followed by sensitivity and correlation analyses of the SIs. TPC-modified binder showed a good storage stability performance with sulfur (at 0.3% optimum dosage) and PPA (at 1% optimum dosage). Remixing resulted in further enhancement in the storage stability performance of TPC-modified binders. The results of the study are quite useful considering the practical usage of TPC for a storage-stable modification of asphalt binder. [ABSTRACT FROM AUTHOR]

The crumb rubber (CR) derived from waste tires has been used widely to prepare rubberized asphalt for paving applications. However, rubberized asphalt severely suffers from poor compatibility and consequent storage instability. Therefore, a solution soaking pretreatment was used to activate the CR surface to improve the compatibility of rubberized asphalt in this study. Three different solutions—water, sodium hydroxide, and sulfuric acid—were employed. The Fourier-transform infrared spectroscopy (FTIR) spectra indicated the removal of zinc stearate from the CR surface after solution soaking. Consequent improvement of the surface hydrophilicity of CR was found from the promoted sedimentation in water and the reduced water contact angle. Dynamic dhear rheometer (DSR) test results showed that the effect of solution soaking on the rheology of rubberized asphalt was slight. However, according to the results of the segregation test and a novel drainage-based method, the solution soaking pretreatments significantly improved the compatibility of rubberized asphalt. This was reflected directly in the reduced segregation degree and promoted CR/asphalt interactions. The solution soaking pretreatment of CR had no adverse effect on the moisture susceptibility of rubberized asphalt according to the modified binder bonding strength (BBS) test results. Of the three pretreatments, sodium hydroxide performed best, followed by sulfuric acid and water. [ABSTRACT FROM AUTHOR]

Due to the increase in the number of vehicles on the road, the amount of used vehicle tires has also increased exponentially. Making tires into rubber powder and adding them into asphalt, which forms asphalt rubber as a kind of asphalt binder of asphalt pavement surface, is an effective way of using waste tires. Styrenic block copolymers (SBS) can improve high-temperature performance of asphalt as a kind of polymer additive. Comprehensive recycling rubber powder and SBS in asphalt mixture can not only make use of waste tires, but also expand the application of waste materials and compose environmentally friendly mixture for the asphalt pavement surface, which improves service life and service function of asphalt pavements. In order to evaluate the high-temperature performance improvement of composite-modified asphalt material, three different asphalt binders and two different asphalt mixture types were selected and the related tests were conducted. The results show that for the mixture of SMA-13 and SMA-16, composite-modified asphalt mixture had better high-temperature performance than asphalt rubber mixture, but worse than SBS asphalt. In addition, the crumb rubber (CR)/SBS composite-modified asphalt had a large internal friction angle, which could give better cohesive force for aggregate gradation. Finally, CR/SBS composite-modified asphalt had the smallest reduction rate from 50°C to 70°C. This study identifies that compound action of rubber powder and SBS is an optimal choice for asphalt pavement surface in high-temperature season. It provides a wider range of applications for asphalt rubber in the road construction field, which also realizes waste cyclic utilization and environmental protection. [ABSTRACT FROM AUTHOR]

A new approach to incorporate scrap tire material into concrete was investigated, in which two reclaimed waste tire components, carbon black and fuel oil, were used to replace a portion of water. The effect of liquid tire content to water ratios from 5% to 40% on an otherwise typical concrete mix were assessed, and compressive and flexural strength, flexural toughness, modulus of elasticity, and several fresh concrete properties were determined. Results were compared with typically expected results of traditional shredded tire mixes with equivalent tire content. It was found that the liquid tire mixes had significantly smaller losses of compressive strength and workability than did shredded rubber mixes; increased flexural strength compared with traditional concrete mix; and significantly decreased stiffness compared with traditional and shredded tire mixes. [ABSTRACT FROM AUTHOR]

The interest in the utilization of granular waste materials as construction fills in lieu of quarried natural aggregates has been increasing recently, resulting in more sustainable and cost-effective industry practices being adopted. This study proposes a mixture of coal wash (CW; a by-product of coal mining) and rubber crumbs (RC; shredding of waste rubber tires) as a potential capping composite for railways. A series of cyclic triaxial tests mimicking typical rail traffic loads were conducted on CWRC mixtures with and without rest periods to gain an insightful understanding of the deformation mechanism of rubber particles. It is found that the inclusion of RC increases the axial permanent strain, the volumetric strain, and the damping ratio, and it reduces the resilient modulus, the shear modulus, and the breakage index (BI). Also, it is found that the mixture with RC recovers part of its energy dissipation efficiency after a rest period is applied, reducing the breakage index further even when the number of load cycles increases. Accordingly, a modified equation is proposed to determine the void ratio, capturing the deformation of the rubber. [ABSTRACT FROM AUTHOR]

The safe disposal of waste tires has been seen as having a negative impact on the environment. To mitigate this impact, the components of waste tires can be used in the production of green concrete. This study explores the effects of the curing and drying regime on the mechanical properties and permeation characteristics of concrete containing both crumbed rubber and steel fibers that are removed from waste tires. Five concrete mixes were designed, and concrete cubes, cylinders, and prisms were cast using waste tires extracts. Crumb rubber was treated by submersion in sodium hydroxide and then used to partially replace 10% and 30% of fine aggregates in the concrete mix. Extracted steel fibers were added at the rate of 1% and 2% per volume of each mix. Compressive and indirect splitting tensile as well as flexural strengths were conducted after normal curing while observing several drying conditions. Additionally, air permeability was assessed using a portable apparatus that was developed to assess permeability easily. For the concrete test specimens containing 10% partial replacement of fine aggregate by crumb rubber and 1% steel fibers, it was discovered that the splitting tensile strength and flexural strength were higher than that of the control mix by 21% and 22.6%, respectively. For specimens that included the 10% crumb rubber and 1% steel fibers, when exposed to oven drying at 105°C for 12 h, the compressive strength results increased by 17% compared with the control specimens exposed to the same conditions. Unlike the compressive strength results, the splitting tensile and flexural strength results decreased after exposing the specimens to elevated temperature. The addition of crumb rubber and steel fibers as a partial fine-aggregate replacement resulted in increasing the air permeability of the concrete to different degrees depending on the percentages used. The oven-drying curing regime improved the permeability by reducing it in specimens containing the 10% crumb rubber and 1% steel fibers as indicated by increasing their permeability time index by 15% when compared with air-dried specimens. Using waste tire extracts as a partial replacement of concrete fine aggregate can be recommended for both indoor and outdoor applications. This study showed that this was a viable, economic, and environmentally friendly method for reducing carbon footprint. [ABSTRACT FROM AUTHOR]

In recent times, alternative ways to dispose various wastes generated, namely, fly ash, scrap tires, steel or iron slag, and foundry sand, are on the rise. Owing to low unit weight and good hydraulic conductivity properties of waste tires, they are found to be a competent alternative fill material for geotechnical applications. Likewise, fly ash is an accepted foundation as well as a backfill material. In the present study, reinforcing composite material made up of fly ash and granulated waste rubber of a nominal size equal to 9.5 mm is explored for use as a reinforced fill material or as a foundation bed material. Accordingly, the interface shear stress properties of a geosynthetic reinforcement with this new composite fill material are obtained using an interface shear box of dimensions equal to 305×305×204 mm (length×width×depth). Two different types of geogrids, uniaxial and biaxial geogrids made up of polyester and polypropylene, are used as a reinforcing material. The granulated rubber contents in the mixtures are varied as 0%, 9%, 23%, 37%, 50%, and 100% to study its effect on the interfacial shear strength of geogrid and mixture. In addition, the effects of the type of the geogrid, tensile strength of the geogrid, and area of aperture opening within the grid are studied for a given mix of fly ash and granulated rubber (50∶50 by total weight of the mixture). The effects of the type of geogrid and tensile strength of the geogrid on the interfacial shear strength are found to be insignificant, while a geogrid with a higher aperture opening area ratio is found to exhibit a high interfacial shear strength. The interaction coefficients of uniaxial and biaxial geogrids with fly ash and granulated rubber mixtures are found to range from 0.74 to 1.16 and 0.74 to 1.18, respectively. [ABSTRACT FROM AUTHOR]

The effect of ethylene vinyl acetate (EVA) on the aging properties and rheological properties of rubberized asphalt was measured in this paper to identify the optimum proportion of EVA combined with waste tire rubber (WTR) modified asphalt. Aging methods of thin-film oven test (TFOT) and pressure aging vessel test (PAV) were conducted to imitate the different degrees of the aging process. At first, frequency sweep at different temperatures was carried out to construct the construction of G* master curves, following the time-temperature superposition principle, to evaluate the aging sensitivity. The black diagram was depicted to compare the rheological behavior of different asphalt binders. The calculation of the WLF equation based on the shift factor of master curves was conducted to calculate the values and aging index of 15°C DSRFn to assess the resistance to fatigue cracking at the intermediate temperature. Then, zero shear viscosity (ZSV) and rutting factor (G*/sinδ) at 60°C were also used to calculate the aging index, because these both are measurements of resistance to rutting deformation at high temperature. Finally, the microstructure of unaged and aged asphalt binder was studied by Fourier transform infrared spectroscopy (FTIR). The relationship between rheological and chemical indexes was studied. The results show that 15%WTR+4%EVA has the best antiaging performance, and EVA can reduce the aging sensitivity of different parameters, especially in the high-temperature area. [ABSTRACT FROM AUTHOR]

In modern waste-management systems, an advantage is given to waste recycling and reuse, rather than to disposal. In the perspective of various initiatives taken worldwide in an attempt to convert waste materials into new products, the objective of this paper is to quantify contribution of unsorted recycled steel fibers from waste tires (RTSF) for use in the concrete industry. An environmentally and financially sustainable hybrid fiber–reinforced concrete (SHFRC), obtained by combining traditional components [manufactured steel fibers (M)] and unsorted RTSF is developed. This paper for the first time, demonstrates that by determining the optimal amount and ratio of fibers (M and RTSF), sustainable hybrid fiber–reinforced concrete (SHFRC) with equal or better properties compared to ordinary fiber-reinforced concrete with only M fibers can be prepared. At the same time, it is also shown that in the optimum quantity and correct ratio, synergy between RTSF and M fibers can be used even for preparation of SHFRC with deflection-hardening behavior. A crack width–deflection model for SHFRC with unsorted RTSF under four-point loading is proposed. [ABSTRACT FROM AUTHOR]

The use of recycled steel fibers from waste tires as reinforcement in concrete matrix appears to be a promising solution, thanks to the performance of the material in terms of toughness and postcracking behavior. The main objective of this paper is to analyze the bond behavior of recycled steel fiber-reinforced concrete (RSFRC) and steel bars, and compare the results with those of industrial steel fiber-reinforced concrete (ISFRC). The paper focuses on the characterization of the mechanical properties of concrete reinforced with short steel fibers from waste tires and on the results of pull-out tests executed both on RSFRC and ISFRC. The experimental results, in terms of failure mode, maximum bond stress, and bond stress versus slip behavior are analyzed and discussed. Finally, a theoretical analysis of the bond-slip behavior was performed. The experimental results show that most of the known performance of the ISFRC can be extended to RSFRC. Referring to the bond performance, an improved behavior of RSFRC with respect to ISFRC in terms of bond-slip law was observed. [ABSTRACT FROM AUTHOR]

The consumption of waste tire rubber in concrete has gained more attention from the point of view of enhanced engineering properties of the product, and also sustainability. Numerous attempts have been stated on the use of waste tire rubbers for the replacement of fine and coarse aggregates in concrete but there is vital need to comprehensively investigate the effect of them on the mechanical properties of rubberized concrete (RC). The aim of this paper is to explore the effect of rubber types and rubber content on mechanical properties of concrete. The compressive strength, tensile strength, flexural strength, modulus of elasticity, strain at maximum strength, and compressive stress-strain curves of RC are studied. Extensive databases used for evaluating the mechanical properties of RC include the measured compressive strength of 298 mixtures, measured tensile strength of 90 mixtures, measured flexural strength of 93 mixtures, measured modulus of elasticity of 156 mixtures, and compressive stress-strain curve of 15 mixtures. Three main rubber mixtures are replaced by fine and coarse aggregate in the collected experimental results that are crumb rubber (CR, with dimension of 0.5-5 mm), tire chips (TC, with dimension of 5-25 mm), and combination of crumb rubber and tire chips (CR+TC). The mechanical properties of these three types RC are evaluated and appropriate constitutive relationships are proposed. [ABSTRACT FROM AUTHOR]

This paper presents the evaluation of the optimum mixing ratio of sand-tire chips (STC) mixtures based on void ratio and shearstrength properties. Locally available sand and tire chips of 20 × 10 mm size are adopted. Different STC mixtures, in the range 10-70% by weight of tire chips (TC), are considered, along with pure sand (0% TC) and pure tire chips (100% TC). Specific gravity, density, and large direct shear tests were conducted for various samples. The volume of voids and weight-volume relations were determined from the dry unit weight and specific gravity values obtained for various mixtures. The results showed that the addition of tire chips up to 40% by weight showed significant decrease of void ratio by 43%. Shear-strength properties, like angle of internal friction values, are increased with TC contents up to 30%. Based on experimental results, the optimum percentage of tire chips of the selected size is in the range of 30-40% by weight, which is the equivalent of 50-60% by volume. Further, the STC mixture at the optimum ratio results in lightweight material with 20% less unit weight with better strength parameters and compressibility behavior, which can effectively be used for geoengineering applications. [ABSTRACT FROM AUTHOR]

Tire derived aggregate (TDA) is a recycled fill material produced by cutting scrap tires into pieces ranging in size from 12 to 305 mm. For the last two decades, TDA has been successfully used in various projects such as embankments, bridge abutments, subgrade insulation for roads, vibration mitigation for rail lines, and landfill daily cover. The material properties of TDA are necessary for the planning and design of such projects; however, there is limited information available, especially for large-size TDA (maximum particle size =75 mm). Large-size TDA is typically used as lightweight fill material for embankments, foundations, and retaining walls. In this paper, the material properties of large-size TDA, as collected from published sources and recently completed material tests, are presented and discussed. These properties include unit weight, shear strength, compressibility, and lateral earth pressure coefficient. In addition, several civil engineering projects are discussed and compared to highlight the use of TDA in state-of-the-art applications. [ABSTRACT FROM AUTHOR]

Scrap tire disposal has been a critical environmental problem in many urban cities due to the huge increase in the number of vehicles. Significant research efforts have been devoted in recent years to explore the use of scrap tires in civil engineering application, as reuse or recycling of scrap tires is the preferred option from a waste management perspective. This paper investigates shear and compressibility behavior of sand-tire crumb (S-TC) mixtures for their application in civil engineering projects. Unlike other studies where tire chips or tire shreds were used, shear strength of the S-TC mixtures has been found to decrease with the increase in the amount of tire crumbs in the mixtures. Significant increase in axial strain corresponding to peak deviator stress has been observed. This can be related to the ductility capacity of the mixtures, as confirmed by brittleness tests. It has also been observed that a larger proportion of plastic strain develops after the first cycle of unloading, and hence the settlement associated with the application of the mixtures can be significantly reduced by preloading. [ABSTRACT FROM AUTHOR]

In recent years, the use of rubber from scrap tires to modify the mechanical properties of bituminous mixes has become increasingly important in road engineering. There is currently much research devoted to the influence of this waste material on mix performance. This paper presents a study of the incorporation of crumb rubber (by the dry process and the wet process) and its effect on the bearing capacity and cohesion of bituminous mixes. The results obtained show that crumb rubber increased the stiffness and stability of mixes although it slightly reduced their indirect tensile strength. Apart from the evident environmental benefits, adding this waste to asphalt mixes improves the long-term performance of road surfaces because it reduces the effect of traffic loads on the pavement. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the use of crumb rubber (CR) from waste tires and engineered additives as a rejuvenator to high reclaimed asphalt pavement (RAP) content asphalt mixtures. Six asphalt mixtures were prepared by mixing aggregate blends with four asphalt binders, an unmodified asphalt binder classified as performance grade (PG) 64-22, two polymer-modified binders classified as PG 70-22M and PG 76-22M, and a PG 76-22 crumb-rubber-modified binder. The RAP content was varied from 0-40% and crumb-rubber additives were blended with the unmodified binder by using wet and dry processes. Hot-mix asphalt (HMA) mixture testing included an evaluation of rutting susceptibility, moisture resistance, and resistance to cracking using the flow number test, the loaded-wheel tracking test, the dynamic modulus test, the modified Lottman test, the dissipated creep strain energy test, and the semi-circular bending test. Results of the experimental program indicated that the addition of the CR additives rejuvenated the blended asphalt binder for the HMA mixture with high RAP content. The use of high RAP content with crumb rubber as a rejuvenator in the preparation of HMA is expected to provide adequate moisture resistance and superior rutting resistance as compared to conventional mixtures. However, because of the hardening properties of the mix prepared with high RAP content, the fracture and cracking resistance of the produced mixture was reduced compared with polymer-modified mixes. [ABSTRACT FROM AUTHOR]

Waste tire rubber constitute a serious worldwide problem due to the lack of landfills and the health hazards associated with these landfills. In addition to the environmental motivation for providing a means of recycling large quantities of waste tire rubbers, the use of tire rubber particles provides a new type of concrete that has unique mechanical and fracture criteria. This paper presents the results of recent experimental investigations on rubber concrete. Chipped and crumbed tire rubber particles were used to replace coarse and fine aggregate with different volume replacement levels. The mechanical and fracture properties of rubber concrete were examined. Quasi-brittle fracture mechanics models are used to determine the effect of incorporating tire rubber particles on the fracture performance of rubber concrete. Finally, some microstructural features of rubber concrete are also reported. It is concluded that the choice of the optimal replacement ratio of the tire rubber particles can yield concretes with desirable strength and fracture toughness criteria for different applications. [ABSTRACT FROM AUTHOR]

This paper presents a large-scale direct shear testing of tire-derived aggregate (TDA) of large sizes (25-75 mm). The objective of this research is to obtain and compare the shear resistances of large-sized TDA and TDA in contact with sand, concrete, and geosynthetics. TDAs are pieces of processed and shredded waste tires that can be used as lightweight and quick fills for embankments, subgrades, and retaining walls. A large-scale direct shear apparatus was designed and constructed. The shear box dimensions were 79 cm wide, 80 cm long, and 122 cm tall. The lower shear box was driven by a hydraulic piston, while the upper shear box remained stationary. The horizontal shear forces, shear displacements, and vertical forces were recorded by an automatic data acquisition system. Three normal loads were applied on the TDA to simulate overburden pressures of 24, 48, and 96 kPa (or 500, 1,000, and ). Duplicate tests were performed to verify the repeatability. The control tests using sand proved that the equipment could obtain comparable and slightly conservative shear strength. The Mohr-Coulomb failure criterion was used to obtain the cohesion (or adhesion) and friction angles of the TDA. The shear testing revealed the difference of failure mechanisms of TDA and sand. For TDA, no peak shear resistance was observed during the entire shearing, and shear resistance continued to increase until the test was terminated at sufficient shear displacement. Further analysis revealed that the shear strength parameters of TDA increase with shear deformation; this represents a challenge in selecting the design parameters of TDAs. The shear strengths of TDA and TDA in contact with other materials are dictated primarily by friction. The friction angles of TDA, TDA on sand, and TDA on concrete are very similar (in a range of 35-39°). [ABSTRACT FROM AUTHOR]